A monolithically integrated smart pixel using an MSM-PD, MESFET's, and a VCSEL

We have developed a smart pixel that monolithically integrates a metal-semiconductor-metal (MSM) photodetector, metal-semiconductor field effect transistors (MESFET's), and a vertical-cavity surface-emitting laser (VCSEL). This device can perform both NOR- and OR-types of operation with a thresholding function. Optimal device parameters are obtained by using a SPICE simulation. Calculations show that the switching time is mainly limited by the CR time constant of the input stage, which consists of the MSM photodetector, the load-resistor, and the MESFET connected to the MSM photodetector. The fabricated device attained a contrast ratio of more than 30 dB with optical gain. The 3-dB bandwidth was 220 MHz and the switching energy was 700 fJ at an operation frequency of 100 MHz. We also discuss the power consumption and the packing density of the smart pixel including the VCSEL as a function of operation frequency. A MESFET that has high f/sub T/ with low bias voltage and a VCSEL that has a low threshold current while maintaining the wall-plug efficiency are necessary to obtain a higher performance device.